Interpretive Summary: Nutrient management and application sites are subject to nutrient buildup from storage, treatment and repeated application of manure. Traditional methods of survey and analysis of nutrient management sites can be costly and time consuming. Methods are needed to quickly assess a site or field location to survey nutrient levels and estimate risk potential. Electromagnetic (EM) soil conductivity methods have been shown to be sensitive to areas of high nutrient levels and offer promise to provide field assessments. This report shows how the EM can be used as a sensor and electronically combined with satellite tracking equipment to form a map of an entire field. The cornfield has been used to compare various manure and compost rates for replacement of commercial fertilizer with the same field treatment assignments for four years. Electromagnetic conductivity maps of treatment areas have shown that the approach can discriminate between treatments (consisting of differing rates of compost, feedlot manure and commercial fertilizer). Strong correlations were found between EM measures and nutrients commonly associated with nutrients in feedlot cattle manure. The high density survey methods generated field maps that allowed visual interpretation to be made of potential areas of nutrient build-up. These maps also may prove useful in precision farming methods as linkages to nutrient application maps.

Technical Abstract:
Electromagnetic (EM) conductivity methods have been shown to be sensitive to areas of high nutrient levels and offer promise to provide field assessments. In this report high density electromagnetic field mapping is described as a method to isolate and detect areas of nutrient build-up in a cornfield receiving waste management research treatments. The cornfield has sbeen used to compare various manure and compost rates for replacement of commercial fertilizer with the same field treatment assignments for four years. High density electromagnetic conductivity maps of treatment areas have shown that EM conductivity measurements were able to differentiate (P<0.0001) a nitrogen check treatment (commercial application rate) versus manure applied at the recommended phosphorus rate, compost applied at the phosphorus rate and compost applied at the nitrogen rate. A nitrogen check treatment and the manure applied at the nitrogen rate treatment resulted in nnearly identical mean values for EM readings and were not statistically distinguishable. Analysis of soil cores (NO3, Cl, P, K, SO4, NH4, Na, electrical conductivity and soil moisture content) randomly located within each treatment were compared to EM readings at the same locations. The Pearson correlation coefficients revealed strong (P=0.02 or better) correlations for all constituents except NH4 (P=0.79). The high density survey methods generated field maps that allowed visual interpretation to be made of potential areas of nutrient buildup.